Diesel cars on our roads are by no means uncommon. In the countries of Western Europe there are a majority of them. Diesel ICEs have several advantages over gasoline. But at the same time there are some disadvantages. What is this motor, what are the diesel engine and the principle of operation? Consider in our article today.
General device
This engine has the same device as the gasoline. So, here is present:
- Cylinder block.
- Head.
- Crank mechanism.
The main difference between a diesel engine and gasoline is the fuel system. If at the last fuel supply is carried out thanks to a mechanical or submersible pump, then the injection pump is used in the diesel engine. There are also nozzles, and there are no spark plugs.
It must also be said that the load on the working elements of the diesel engine is higher. Therefore, all its components are reinforced.
Please note that modern diesel engines can be equipped with glow plugs. Some confuse them with spark plugs, but these are completely different things. In diesel cars, they are used to heat cold air in cylinders. So, an easier start-up of ICE in the winter is carried out.
The injection system itself on modern diesel engines is direct. On older engines, ignition occurred in a special pre-chamber. The latter is a small cavity above the main combustion chamber with several openings through which oxygen enters.
Features
Among the features of this power unit, it is worth noting the degree of compression. They are twice as high as that of a gasoline engine. In view of this, the diesel engine has a special piston design. Their bottom is determined by the type of combustion chamber. The piston bottom itself is higher relative to the upper plane of the cylinder block at TDC.
Another point is the ignition method. As we said earlier, there are no familiar candles. But how does fuel ignite? The working mixture is ignited by the high temperature in the chamber, which is achieved after compression by the air piston.
The principle of operation of the diesel fuel injection pump
The high pressure pump receives fuel that is pumped by the low pressure booster pump from the tank. In a certain sequence, the injection pump pumps a portion of fuel into the nozzle line for each cylinder. These nozzles can only open when exposed to high pressure in the line. When lowering its nozzles are closed.
How does a diesel engine work?
Consider the principle of the diesel engine. Its essence is the compression ignition of the fuel in the chamber when mixed with heated air.
The feed itself is carried out separately. So, first air is forced into the cylinder. Further, the piston begins to move upward and in the TDC position, fuel is injected through the nozzle. In the process of compression, the air is heated to high temperatures (about 800 degrees Celsius). And the fuel comes under a pressure of 30 MPa.
Then the mixture ignites spontaneously. This causes the piston to lower down. So, a working stroke is made - energy is transmitted to the crankshaft, as well as the flywheel. After a working cycle, the combustion products exit through the exhaust windows by blowing. Then the gases through the muffler enter the atmosphere. But on modern engines, gases can undergo re-circulation. The operating principle of the USR on a diesel engine will be considered a little later.
Thus, the work cycle includes four cycles. These are inlet, compression, stroke and exhaust. This is exactly the principle of operation in a four-stroke diesel engine. It must be said that fuel consumption depends on the correctness of its action. So, in a normal state, a poor mixture is used , which can significantly save on consumption.
Varieties of pumps
There are two types of injection pumps:
The first type includes separate sections. There are as many as the engine cylinders. Each section has a sleeve with an incoming plunger. The latter acts thanks to the cam shaft, which rotates from the engine crankshaft. Sections are arranged in a row. But now this type of injection pump is not used by manufacturers, since such a fuel system does not meet the requirements for noise and environmental friendliness.
Now about the distribution. Such pumps generate much greater pressure and meet all modern requirements. The desired pressure is maintained depending on the current operating mode of the engine. In the design of such a pump there is one plunger-distributor. He performs translational movements to supply fuel and rotational to distribute it across the nozzles of each of the cylinders.
Among the advantages of such pumps, it is worth highlighting small overall dimensions, low noise level, as well as stable operation at high engine speeds. At the same time, such a diesel engine is finicky in fuel quality. All parts in the pump are lubricated with fuel, and the gaps are critically small. The slightest pollution provokes unstable engine operation and may lead to the repair of fuel equipment.
About the Common Rail System
More than ten years ago, automakers began to produce cars with the Common Rail system. What it is? This is direct injection of fuel under high pressure. This system provides an increase in torque and power, as well as good fuel efficiency.
Consider the principle of operation of the Common Rail diesel injection system. The principle is based on the supply of fuel to the injectors from the ramp. The pressure in it is maintained regardless of the speed of the crankshaft. Fuel injection is carried out by injectors at the command of the EDC controller. Special magnetic solenoids are built into it. The controller operates thanks to control signals from the electronic control unit.
Among the features of the injection system, it is worth noting the battery pack. It includes:
- Nozzles
- Distribution pipe.
- Fuel supply line.
So, the control unit according to a given algorithm transmits a signal to the solenoids. And then the nozzle injects fuel into the chamber. Such a scheme allows to achieve high precision control of the combustion process. As for pressure, it can reach up to 2.5 atmospheres, which is very serious. So, fuel burns with maximum efficiency. This allows you to increase engine torque. And thanks to the exact dosage, fuel consumption is reduced and gas toxicity is reduced.
Recirculation system
This system is used on all diesel cars that meet Euro-4 requirements. It is also called the USR. So, this system performs the removal of a certain amount of exhaust gases from the collector in front of the turbine and transfers them to the channel in front of the intake manifold.
The system is a special valve and several nozzles for exhaust gases. The first performs exhaust bypass and is distinguished by an electric drive. On some engines, the EGR valve has a pneumatic actuator.
Consider the operating principle of the EGR valve on a diesel engine. It is based on a vacuum, which is produced by a special vacuum pump. The level of vacuum is regulated by a special solenoid valve.
The operating principle of the diesel recirculation system is simple. So, the electronic control unit receives data from the sensors and evaluates the situation about the operation of the internal combustion engine in all modes. Next, the valve is opened or closed to supply exhaust gas to the manifold. This leads to a decrease in oxygen concentration and a decrease in the rate of combustion of the mixture in the chamber. As a result, the combustion temperature is reduced and the formation of harmful oxides is reduced. So, the system allows to reduce the toxicity of gases even when the internal combustion engine is running on a lean mixture.
Diesel advantages
Consider the advantages of these engines. The first and most important plus is profitability. Since the diesel engine has a slightly different operating principle (operates on a lean mixture), the internal combustion engine can consume one and a half times less fuel than gasoline, with the same volume.
At the same time, the motor produces good torque, which is important during acceleration. Another plus is that the torque shelf is wide enough. Traction is available literally from idle. Gasoline sometimes has to untwist up to five thousand.
Diesel disadvantages
Since the principle of operation of a diesel engine is based on self-ignition of a mixture, it is difficult to start such engines in cold weather. Yes, for this they came up with special glow plugs. But again, they are not on all engines, and sometimes there are problems with them.
One of the most serious drawbacks is the cost of maintenance. The most expensive part is the fuel equipment. If it becomes worthless, it is worth preparing for a serious investment. It is very difficult to repair nozzles or the fuel pump yourself. This requires skills and specialized equipment.
Among other disadvantages, it is worth noting the increased noise. No matter how technologically advanced the diesel engine, it will still work louder than gasoline. This is one of the main reasons why car manufacturers have not switched to diesel engines for so long.
Another drawback is the high requirements for fuel and consumables. If we talk about modern diesel engines in which the high-pressure fuel pump is lubricated by the fuel itself, its quality should be at a level. The same goes for oil. It is recommended to fill in only synthetics, and change - every 10 thousand kilometers.
To summarize
So, we found out what the diesel engine has and how it works. As you can see, with its advantages, this motor is not without a number of disadvantages. But is it worth it to buy a diesel car instead of a gas? As practice shows, the purchase is justified, given the fact that many expenses are offset by miserable fuel consumption.